The present invention is related to prosthetic heart valve replacement, and more particularly to devices, systems, and methods for reducing friction when using catheters and similar devices for transfemoral delivery of collapsible prosthetic heart valves.
Prosthetic heart valves that are collapsible to a relatively small circumferential size can be delivered into a patient less invasively than valves that are not collapsible. For example, a collapsible valve may be delivered into a patient via a tube-like delivery apparatus such as a catheter, a trocar, a laparoscopic instrument, or the like. This collapsibility can avoid the need for a more invasive procedure such as full open-chest, open-heart surgery.
Collapsible prosthetic heart valves typically take the form of a valve structure mounted on a stent. To place such a valve into a delivery apparatus and ultimately into a patient, the valve must first be collapsed or crimped to reduce its circumferential size. For example, a conventional stent is typically collapsed and inserted into a distal sheath for delivery into a patient, for example, through a femoral artery.
When a collapsed prosthetic valve has reached the desired implant site in the patient (e.g., at or near the annulus of the patient's heart valve that is to be replaced by the prosthetic valve), the prosthetic valve can be released from the delivery apparatus and re-expanded to full operating size by unsheathing the stent containing the valve.
Despite the various improvements that have been made to the collapsible prosthetic heart valve delivery process, conventional delivery devices, systems, and methods suffer from some shortcomings.
In conventional transfemoral valve delivery devices, the distal sheath of the delivery device must have an inner diameter sufficiently large (e.g., a size of about 16 French) to cover a collapsed prosthetic heart valve, while the outer shaft of the delivery device that extends between the distal sheath and the handle must have a diameter sufficiently small (e.g., a size of about 12 French) to allow the outer shaft enough flexibility to bend around the aortic arch. When such a device is inserted into the femoral artery through an introducer, a hemostasis valve (e.g., a flat sheet of silicone rubber having a vertical slit and a horizontal slit) admits the distal sheath of the delivery device and seals around the outer shaft of the delivery device to prevent excessive bleeding.
A design tradeoff may exist because the hemostasis valve must be flexible enough to admit the larger distal sheath yet stiff enough to create a seal against the smaller outer shaft. If the hemostasis valve is too flexible, the seal against the outer shaft may be too weak, potentially resulting in excess bleeding. If the hemostasis valve is too stiff, the seal against the outer shaft may be too strong, potentially resulting in high operating friction when a user (e.g., a surgeon or an intervention cardiologist) needs to slide the outer shaft proximally within the hemostasis valve to deploy the heart valve.
If the force required to overcome a high amount of friction between the hemostasis valve and the outer shaft exceeds the force required to deploy the heart valve (i.e., the force required to overcome the friction between the stent portion of the valve and the distal sheath), the user may be forced to deploy the valve by pushing it out of the distal sheath towards the aortic annulus, rather than the preferred method of withdrawing the distal sheath from the heart valve while maintaining the position of the valve at the aortic annulus.
One potential solution to this design tradeoff could be to increase the diameter of the introducer and the hemostasis valve, but too large of an introducer (e.g., a size greater than about 20 French) may make it necessary to perform an additional surgical procedure to seal the entry point into the femoral artery.
Another potential solution to this design tradeoff could be to decrease the outer diameter of the distal sheath (e.g., to a size less than about 18 French), thereby allowing the use of an introducer and hemostasis valve having a smaller diameter. However, the distal sheath must accommodate a collapsible valve that is large enough to properly fit in the aortic annulus. Even in a collapsed state, a typical valve has a size of about 16 French, so a typical distal sheath must have an outer diameter size of at least about 18 French to accept a 16 French collapsed state implant, and a typical introducer must have an inner diameter sufficient to accept an 18 French outer diameter device.
There therefore is a need for further improvements to the devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves. Among other advantages, the present invention may address one or more of these shortcomings.